This invention relates to steels, and, more particularly, to a steel that achieves good structural properties with low alloying and production costs.
Low-alloy steels are iron-based metallic alloys, containing additional alloying elements in amounts of up to about 2 percent by weight, that are used in a wide variety of applications. Such steels typically have good mechanical and physical properties, generally low cost, and a high degree of versatility. Their properties can be varied over wide ranges by adjusting the alloying elements and processing of the steel to its final form.
The present invention deals with steels used in structural applications, such as plates. Such steels have medium levels of alloying elements that are, on the whole, relatively inexpensive. They are processed by casting and hot rolling, sometimes with accelerated cooling after rolling to improve the final mechanical properties. The properties of the final processed steel pieces depend upon their composition, processing, and final thickness. Thinner sections usually have properties superior to those of otherwise identical, but thicker, sections.
To improve the uniformity of specifying and obtaining steels, standards have been established for these and other types of steels by organizations such as the American Society for Testing and Materials (ASTM). In one example of interest here, ASTM Specification A572 sets forth the chemical and physical standards for steels that must achieve specified minimum yield strengths of 50 KSI in plate sections ranging from about 1/2 to 2 inch thick sections, termed the ASTM A572, Grade 50 standard. Structural designers utilize these standards in ordering steel from suppliers.
The various steel standards typically specify property levels that must be attained and maximum levels of alloying elements, but not minimum levels of alloying elements. A continuing effort by steelmakers is therefore to develop steels that meet the property requirements of the standards, but with reduced cost as a consequence of using reduced levels of the more expensive alloying elements. In particular, it would be desirable to develop a steel that meets ASTM A572 Grade 50 properties, but at lower costs than possible with the existing steels used for this grade. The present invention provides such steels, and their processing.